Symmetries and dualities in non-supersymmetric CHL strings

We chart the classical moduli space of heterotic strings with broken supersymmetry a la Scherk-Schwarz and gauge group rank reduced by 8 in eight dimensions. This space consists of four connected components, each with its own characteristic spectrum and T-duality group. Three of these components uplift to nine dimensions and can be described as Coxeter polyhedra, allowing an exact characterization of their maximal symmetry enhancements and decompactification limits. We determine the maximal enhancements in the eight dimensional theories using lattice based algorithms in the bosonic formulation, and perform an indepth analysis of their massless spectra. Finally we argue that one component has a supersymmetric $\mathcal{N}=1$ sector described by BPS objects at strong coupling in a non-supersymmetric version of the type IIB string on $T^2\mathrm{/}{\mathbb{Z}}_2$ with one $O{7}^{+}$-plane.